(CNN) -- A double decker bus careened off a major highway and crashed into a ditch near Guatemala City Friday night, killing at least 57 people and injuring another 40, according to emergency officials.

The bus, carrying about 100 people from Guatemala City bound for San Salvador, was "just a bunch of metal," journalist Martin Austurias said at the scene.

A makeshift morgue was set up along the four-lane highway so that relatives of the dead could help identify the victims, Austurias said.

The bus was traveling down a hill about 30 miles outside of Guatemala City when it crossed the median into oncoming traffic and then plunged into the ditch, he said.

Dozens of police and firefighters were on the scene working to recover bodies from the gruesome wreckage, he said.E-mail to a friend